I have a nice set of Campy brake calipers, but the mounting bolt threads are screwed up. I need to buy a die to chase the threads. Does anyone know the correct thread size and pitch?

That would be M6x 1mm

Take the nut to a hardware store, and they should be able to find and give you the appropriate bolt. Ace Hardware?

I have a nice mom-and-pop neighborhood hardware store nearby. I recently took the broken, rusted nut from my brake caliper, and the generous owner took a minute of his time to help me find the appropriate thread and size nut and bolt. They sell nuts and bolts loose. I think I spent about a buck, or a buck and a half, for both the bolt and nut. Well, the bolt was a tad longer than the stock one.

Couple problems:

1. the bolt is chrome-plated, which kills cutting tools.
2. (recycling some verbiage I wrote in a different thread) The problem is, how do you start a threading die on a screw with the first couple threads mangled? There's no way to start it in-phase with the good threads farther down, so the die will probably start cutting out of phase with the good threads, and ruin all the threads, even the previously-good ones. I'm not even talking about the problem of starting the die aligned with the axis of the part; that can be achieved on a lathe, or with some sort of custom-made pilot on the die holder (but you have to make the pilot, it's not a stock part anyone sells). But no amount of skill or technology will overcome this phasing problem; only blind luck will save you, maybe one out of a thousand tries.

Of course your threads might be only a little damaged, and the die might start straight and in-phase; then you'd only have the chrome problem. If the die isn't too expensive, maybe worth a try.

But me, even though I have the die, I'd probably re-shape the bad threads with a triangle file, and magnifiers to see what I'm doing. Optivisor FTW! Maybe if your eyes are younger than mine you can do it without magnification. I know a real Optivisor is kind of expensive, but there are generics that are much cheaper.

Pro tip: attach a small headlamp to the Optivisor, for bright light right where you're looking. Not the kind made for outdoor use like jogging at might, they have a narrow beam. For close-up work, you want a flood or "floody" beam shape, else the little spot of light is never right where you're looking. I use a Zebralight. Expensive, but they will change your life, so useful in the shop I use mine every day. (Again, knock-offs can be much cheaper, if you don't need Zebralight-level quality.) I have several, and one stays attached to the Optivisor with zip ties. If you get the type that takes a 18650 lithium battery (longest lasting), you'll also need a charger for 18650s, and probably at least two cells so you always have one charged.

A cheap solution is to get a stainless steel nut of the correct size and use a needle file to cut a slot in its thread. That slot is often enough to work like a threading die and improve the threads.

Stainless is soft - especially the mystery metal cheap fasteners from China. The home made improvised die should be IMHO a Grade 5 or 8 regular steel nut. You'll probably need a tiny carbide burr to cut a groove in them.

Why not just ask for a functional pivot bolt? I have a bunch of these, this would be cheaper than a die! Jim Merz

https://boulderbicycle.bike/2012-Cam...ice-price.html

$23 plus shipping. Only fits if the one you need is a front, for external (not recessed) nut. Or it sounds like Jim Merz has just the one you need, and his asking prices are always reasonable.

But the OP didn't say what model or vintage of Campy brake, so if it's some more modern brake like a dual-pivot, all bets are off.

General rule: Pics or it didn't happen!

It’s a Nuovo Record front caliper, recessed bolt. I can get the nut started a few good turns then it get to tight to go any further. I’ll get the die and have a go at before I look for alternatives. Thanks

Oh that's good, if the nut starts then the die will too. Good luck!

I've had good luck with the Yoktosun Lighted Head Visor:

https://www.amazon.com/YOCTOSUN-Rech...=sr_1_6?sr=8-6
Affordable, and several magnifiers are included.

I’ve had good outcomes with thread files. Good for various bolt diameters and you can start on the undamaged section of thread and work back towards the damaged end. Nice to have a set in the shop. I’ve not had good outcomes with triangle files.

YMMV

But thread files are more expensive; triangle files are more expendable. The chrome on a Campy brake bolt is very hard and will dull your thread file rapidly if not immediately.

I got lucky, came out perfect.